Numerous methods and apparatus for electrophotography, electrostatic recording and electrostatic printing are known in the art. Typically, a charged photosensitive surface, for example a charged photosensitive drum, is irradiated with an optical image and an electrostatic latent image is formed on the photosensitive surface. In the development process, a developing agent, i.e., toner, is adhered to the electrostatic latent image. Typically, a controlled amount of toner is fed to a developer magnetic roller by a metering blade positioned against the surface of the developing roller. The developer magnetic roller, with the toner on its surface, is typically rotated in a direction opposite to that of the photosensitive drum, and toner adheres to the electrostatic latent image to develop the image. Various toner compositions have been developed in order to provide improved copying, recording and/or printing with such apparatus.
In recent years, there has been a desire to recycle or remanufacture components of commercially available electrostatic copiers, recording devices and printers and particularly to recycle or remanufacture developer cartridges. Generally, the developer cartridges comprise a container for holding toner, a developer magnetic roller and a metering blade for applying an even layer of toner to the roller, and the cartridges are recycled by refilling the container with toner. Oftentimes, the developer magnetic roller in a recycled or remanufactured developer cartridge is worn to some extent so that the surface becomes relatively smooth and/or not sufficiently conductive. Consequently, toner is prevented from moving smoothly and uniformly through the metering blade nip and as a result, "wavy" patterns of toner may form on the developer roller which, in turn, are developed onto the photoconductive drum. Additionally, in some instances, the developer magnetic roller in a recycled or remanufactured developer cartridge is provided with a polymer-based coating to prevent further wear. Typically, the polymer coating which is applied to the developer roller does not have the same properties as the original developer roller surface so that the surface roughness and/or resistivity are altered. As a result, the layer of toner carried on the developer roller will have irregularities which in turn will be evident in the image developed on the photoconductive drum.
Recoated or worn developer magnetic rollers also may exhibit higher resistivities than new developer rollers. As a result, the charge of a layer of toner on the developer roller may be increased as voltage bleed off is prevented. This in turn results in a thin layer of very highly charged toner particles which stick to the recoated or worn developer roller and do not develop onto the drum. The developer roller continues to pick up toner from the hopper; however, the toner is much lower in charge because there is not sufficiently good contact between the second layer of toner and the surface of the developer roller. Consequently, the low charged toner builds up on top of the highly charged toner and creates a wavy pattern on the surface after going through the metering blade nip. Because the second layer of toner is not highly charged, it readily develops onto the drum and then transfers to paper as the aforementioned "wavy" defects.
While many toner compositions are designed for good development in new OEM equipment, oftentimes commercially available toner compositions cannot accommodate the irregularities in the development process caused by recycled or remanufactured developer equipment such as developer cartridges. Accordingly, a need exists for toner compositions which not only provide good development in new electrostatic copying, recording and printing apparatus but are also capable of providing good development when employed in recycled or remanufactured developer cartridges in such apparatus.
Typically, extra-particulate additives are combined with toner particulates in order to improve selected properties of the toner particulates including transferability, cleaning properties, flowability and the like, as taught, for example, in the Akagi et al U.S. Pat. No. 5,296,324 and the Kanbayashi et al U.S. Pat. No. 5,120,631. It has also been suggested to lower the chargeability (tribocharge) of toner compositions in order to improve transferability, cleaning properties, flow problems and the like. However, print quality problems, including low optical density and high CAD, often result. Accordingly, there is a continuing need for improving toner compositions.